210 PHYSIOLOGY CHAI>. 



We have already seen that two periods can be detected in the 

 course of a cardiac revolution, during which the heart develops a 

 negative pressure and exercises aspiration upon the blood issuing 

 from the veins : there is a moment of systolic and a moment of 

 diastolic aspiration (see Fig. 67). The former is confined to the 

 auricles ; the latter extends both to auricles and ventricles. 



When systolic aspiration (as in Fredericq's experiments cited 

 above) takes place with the opened thorax, it must depend on the 

 sudden sinking of the base of the heart in the first period of 

 systolic efflux, which increases the capacity of the diastolic auricle. 

 This is the explanation given by Purkinje (1843), by Nega (1851), 

 and more recently by Chauveau and Lefevre, as well as Fredericq. 

 This aspiration of the auricles has nothing to do with diastolic 

 activity ; it is caused by the systole of the ventricle, which works 

 simultaneously as a pressure pump against the arteries, and as an 

 aspirating pump against the auricles and veins. 



The diastolic aspiration, on the contrary, which coincides with 

 the first period of perisystole, and spreads from the ventricles to the 

 auricles and adjacent veins, does really represent energy developed 

 by the ventricles during diastole. The mechanical effect of 

 diastole is indeed very small as compared with the mechanical 

 effect of systole : but in any case it is sufficient to defend the 

 opinion that the ventricles are active in the first period of peri- 

 systole, and dilate by aspiration, not by the vis a tergo of the 

 blood rushing in from the auricles. The little frog heart is capable 

 in its diastolic distension of overcoming a resistance equal to 

 15-20 mm. of water (Mosso and Pagliani) ; the heart of a dog can 

 dilate, even when pressure is put upon its outer surface, in excess 

 by 20-30 cm. of water of that to which its inner surface is sub- 

 mitted (Stefani). 



Various hypotheses have been put forward to explain the 

 diastolic aspiration, which may be rapidly summarised : 



(a) The pressure within the thoracic cavity is negative even 

 in the expiratory position of the lungs, and becomes more strongly 

 negative during inspiration. 



As early as 1853 Bonders pointed out the importance of this 

 mechanical factor, which serves to facilitate the course of the 

 blood in the intrathoracic veins and the diastolic filling of the 

 heart by aspiration. Yet this does not adequately explain the 

 diastolic aspiration, which can be demonstrated even with the 

 open thorax. Nor does it explain the cardiac aspiration visible 

 with closed thorax, since this is greater in the left than in the right 

 ventricle, and in the latter again than in the auricles, where it 

 should, in consequence of the ready extensibility of the auricular 

 walls, be greatest. 



(&) In 1855 Briicke revived the theory of the auto-regulation 

 of the heart, basing it on the same arguments as already brought 



